ALLOPHONES

In order to understand allophones and how they function, it helps to have a basic understanding of linguistics, the study of language, and phonology (or how sound functions within a language). One of the basic building blocks of language is phonemes. They are the smallest sound units capable of conveying a distinct meaning, such as the s in "sing" and the r of "ring."

Allophones are a kind of phoneme that changes its sound based on how a word is spelled.
Substituting one allophone for another allophone of the same phoneme doesn't lead to a different word, just a different pronunciation of the same word. For this reason, allophones are said to be noncontrastive.